Begin by patting the boneless, skinless chicken breasts dry with paper towels. Generously season both sides with salt, freshly ground black pepper, and dried oregano.

In a heavy-bottom skillet, heat about 2 tablespoons of olive oil over medium-high heat. Add the seasoned chicken breasts and sear for 5–7 minutes on each side until golden brown and cooked through.

In the same skillet, add the diced onion and minced garlic. Sauté for 2–3 minutes until the onion is translucent and the garlic is fragrant.

In a mixing bowl, combine the crushed tomatoes, heavy cream, and grated Parmesan cheese. Whisk until smooth. Pour into the slow cooker.

Place the seared chicken breasts into the slow cooker, ensuring they're coated with the sauce. Cover and set to low for 6–8 hours or high for 3–4 hours.

Once cooking is complete, gently stir the mixture. Adjust seasoning with salt or pepper. Serve over linguine, rice, or greens, garnished with fresh basil leaves and extra Parmesan.